The present invention relates to the particle separating or elutriation art, and more particularly to a method and means for separating fine char from the discharge waste in the process for directly reducing iron oxides in a rotary kiln using a solid carbonaceous reducing agent as both fuel and reductant.
The discharge materials from rotary kilns, wherein materials containing iron oxides and other oxides are directly reduced using solid carbonaceous material such as coal as the fuel and reductant, are conventionally subjected, after screening, to magnetic separation whereby the sponge iron or metal product is magnetically attracted and withdrawn from the materials and the nonmagnetic portion of the materials comprising charred coal and fine matter are passed along and separated. The larger pieces of charred coal or char are recycled back to the kiln, and the fine char is included with the ultimate process waste. The fine char passing to waste can amount to a considerable loss for the process, as additional coal must be fed in time to the kiln in proportion to the char dropped out of the process in the waste. Particularly with recent improvements in the performance of this type of direct reduction process such as disclosed in co-pending application Ser. No. 132,806, the loss of the fine char takes on greater importance as it can now be efficiently recycled by feeding it with or without the coal through the discharge end of the kiln.
To improve the efficiency of this type of process and related processes, the present invention may be used in the product separation system to recover lighter particles, such as the fine char, from heavier waste particles, providing a larger percentage of char recovery and recycling and thus a reduction in the amount of fresh coal required in the process.